A label-free electrochemical immunosensor for direct, signal-on and sensitive pesticide detection

► Direct, label-free electrochemical immunosensor against atrazine. ► Positive current change upon atrazine detection. ► Very low detection limit of ca. 1pM, i.e. 0.2ngL−1, one of the lowest reported for such immunosensors. ► Far lower than the detection limit required by European Union (0.1μgL−1). A new electropolymerizable monomer, [N-(6-(4-hydroxy-6-isopropylamino-1,3,5-triazin-2-ylamino)hexyl) 5-hydroxy-1,4-naphthoquinone-3-propionamide], has been designed for use in a label-free electrochemical immunosensor when polymerized on an electrode and coupled with a monoclonal anti-atrazine antibody. This monomer contains three functional groups: hydroxyl group for electropolymerization, quinone group for its transduction capability, and hydroxyatrazine as bioreceptor element. Square wave voltammetry shows that the polymer film, poly[N-(6-(4-hydroxy-6-isopropylamino-1,3,5-triazin-2-ylamino)hexyl) 5-hydroxy-1,4-naphthoquinone-3-propionamide], presents negative current change following anti-atrazine antibody complexation and positive current change after atrazine addition in solution. This constitutes a direct, label-free and signal-on electrochemical immunosensor, with a very low detection limit of ca. 1pM, i.e. 0.2ngL−1, one of the lowest reported for such immunosensors. This is far lower than the detection limit required by the European Union directives for drinkable water and food samples (0.1μgL−1). The strategy described has great promise for the development of simple, cost-effective and reagentless on-site environmental monitors.